When you create a professional voicemail greeting, it can be a good idea to think about what your callers might want to know. After doing so, you can make a list of points to cover in your voice message; it might also be a good idea to write out the entire greeting on a piece of paper. The ideal message should be somewhere between 10 and 20 seconds, so you may want to time yourself repeating your message before you record it. After composing your telephone message, it can be a good idea to get a second opinion of this greeting so you can make sure it sounds professional. Writing down a voicemail greeting helps prevent mistakes when recording it.
Last but not least a slogan or branding: this is really more important for new customers and people that are calling or leaving a voicemail for the first time rather than returning ones (though it helps a little with them too!). A catchy phrase makes it easier for people to remember your name and recognize you when you give them a call back.

You don’t have to spell out every single thing that you think they might want to know. Have some faith that your callers will be able to figure things out on their own. Be natural but informative.
28. Hey, there. You’ve reached [your name]. Please leave me a brief message about the reason you are calling and your contact information. I will call you right back at the earliest opportunity. Have a nice day!